The present invention pertains to methods for preparing aromatic polymers. More particularly, the present invention pertains to processes for the preparation of polyamide-imides. Polyamide-imides are generally prepared by the reaction of 4-trimellitoyl anhydride chloride with an appropriate diamine as shown below. ##STR4##
In that procedure, an intermediate polyamic acid is cyclized in an imide forming step with the elimination of water. This procedure presents the shortcomings of using moisture sensitive acid chlorides and driving off a small molecule in the imide forming step, which can create voids and defects in the polymer product. Polyamide-imides produced by this procedure have a backbone of alternating amide and imide units.
Japanese Kokai 123823, published May 16, 1989, and Yoneyama et al, Macromolecules, Vol. 21, 1988, pp. 1908-1911 disclose the use of a Heck carbonylation reaction, that is, a transition metal catalyzed carbonylation and coupling, in the preparation of low molecular weight polyamides. U.S. Pat. Nos. 4,933,419; 4,933,466 and 4,933,467 and 4,933,468 disclose methods which utilize Heck carbonylation reactions to produce esters, imides and amide-imides, respectively. Scott, W.J., "Journal of the Chemical Society, Chemical Communications", (1987), 1755 and Mutin, R. et al, "Journal of the Chemical Society, Chemical Communications", (1988), 896, teach palladium catalyzed carbonylation reactions of chloroarenes using Cr(CO).sub.3. Bozell, J.J., et al, "Journal of the American Chemical Society", 110 (1988), 2655, teaches a palladium catalyzed carbonylation reaction of chloroarenes which requires both Ni and Pd catalysts and the presence of NaI.
It is therefore highly desirable to provide improved methods for the preparation of polyamide-imides.
It is also highly desirable to provide improved methods for the preparation of polyamide-imides from preformed imides which utilize a Heck carbonylation reaction rather than a post polymerization cyclization to give the imide structure.
It is also highly desirable to provide improved methods for the preparation of polyamide-imides which avoid the use of hydrolytically unstable acid chlorides.
It is finally highly desirable to provide improved methods for the preparation of polyamide-imides which provide all of the above desired features.